Mammal Craftsmen. 



water at a given level. These dams are really very 

 remarkable structures, often of great length, not in- 

 frequently upwards of one hundred and fifty yards. 

 They run out across the stream from bank to bank, 

 either in a straight line or curved in a bow, according 

 to the character of the stream and the requirements 

 of the Beavers. Like the lodges, they are composed 

 of lengths of timber cut from the trunks and branches 

 of the trees, filled in with smaller sticks, roots, grasses, 

 and moss, and all plastered with mud and clay in the 

 most workman-like manner, until the whole structure 

 is made perfectly water-tight. By means of these 

 dams the Beavers are able to convert even small rivu- 

 lets into large pools of water, often many acres in 

 extent, and dotted about with islands upon which 

 the lodges are constructed. Thus, all unconsciously, 

 the Beavers exercise a considerable influence upon 

 the general aspect of the locality inhabited by them, 

 which may persist long after they themselves have 

 disappeared from those regions. By their constant 

 felling of the trees they gradually produce clearings 

 in the forest often many acres in extent, and the 

 lagoon produced by damming back the water becomes 

 converted into a peat-moss. These peaty Beaver- 

 meadows, as they are called, are still to be traced in 

 many countries where the Beaver no longer exists. 



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